Power tongs are often employed in the oil and gas industry to break-out or make-up threaded connections on tubular members (such as drill pipe, tubing, and casing). It is generally required that one tong grip and rotate one section of a tubular string and a second tong grip and hold stationary the other section of the tubular string. The tong which rotates the section of the tubular member is typically referred to as the power tong, while the tong which holds the other section of the tubular member stationary is typically referred to as the back-up tong. Examples of conventional power tongs can be seen in references such as U.S. Pat. Nos. 5,671,961, 5,702,139, and 5,819,604 to Buck, each of which is incorporated herein by reference in its entirety.
Power tongs typically have two or more jaws which are actuated to grip and release the tubular member. There are generally two types of jaws—pivoting jaws and sliding jaws. Both pivoting jaw and sliding jaw power tongs are well known in the art. An example of a pivoting jaw power tong can be seen in U.S. Pat. No. 4,350,062 to Farr et al., which is incorporated by reference herein. FIG. 1 illustrates the basic components of a typical pivoting jaw power tong 1. A tong body 2 encloses a ring gear 3 which has a cam surface 4. Positioned within ring gear 3 are the pivoting jaws 5. Pivoting jaws 5 are pivotally attached between an upper and lower tong cage plate (not shown) by pivot pin 7. A roller 6 on pivoting jaws 5 engages cam surface 4 on ring gear 3. As is well known in the art, the rotation of ring gear 3 causes different sections of cam surface 4 to either push roller 6 toward tubular member 100 (causing the jaws to grip the tubular member) or allow roller 6 to move away from tubular member 100 (causing the jaws to release the tubular member).
An example of a sliding jaw power tong may be seen in U.S. Pat. No. 5,435,213 to Buck, which is incorporated by reference herein in its entirety. A sliding jaw power tong has a tong body and ring gear structure similar to a pivoting jaw power tong, but the jaw is not pinned to the cage plates. The sliding jaw is moved radially toward the tubular member by way of the ring gear's cam surfaces acting on the sliding jaws' rollers. Sliding jaws could also include radially moving jaw arrangements such as seen in U.S. patent application Ser. No. 10/421,041, filed on Apr. 23, 2003 to Bangert, entitled Improved Tong Piston and Cylinder Assembly, which is incorporated herein in its entirety.
Actual contact with the tubular member is typically accomplished through the use of die inserts which are removably positioned in the power tong jaws. Typical die inserts have gripping surfaces which contain a number of ridges or teeth, or have alternative gripping surfaces such as those disclosed in U.S. Pat. No. 6,378,399 to Bangert, which is incorporated by reference herein in its entirety. When the jaws close upon the tubular member, the teeth firmly “bite” into the tubular member and prevent slippage when torque is applied. In most conventional tong jaw systems, the jaws are designed to grip a tubular member of a particular nominal diameter (or a limited range of nominal diameters) and the dies are in a fixed orientation relative to the jaw body. The dies are positioned on the jaw at an angle to maximize the contact between the face of the die and the surface of the tubular member. Because the diameters of tubular members are allowed to vary within certain tolerances, the exact diameter of the tubular member being gripped can vary, especially when dealing with large diameter tubular members. Particularly in the case of prior art pivoting jaw systems, differing diameters may prevent all of the dies from squarely engaging the surface of the tubular member and in extreme cases may completely prevent one or more of the dies from contacting the surface of the tubular member.